feat(core): allow plugins to self-disable by returning null

packages/docusaurus-plugin-client-redirects/src/index.ts

@@ -21,15 +21,15 @@ const PluginName = 'docusaurus-plugin-client-redirects';
 export default function pluginClientRedirectsPages(
   context: LoadContext,
   options: PluginOptions,
-): Plugin<void> {
+): Plugin<void> | null {
   const {trailingSlash} = context.siteConfig;
   const router = context.siteConfig.future.experimental_router;
 
   if (router === 'hash') {
     logger.warn(
       `${PluginName} does not support the Hash Router and will be disabled.`,
     );
-    return {name: PluginName};
+    return null;
   }
 
   return {

packages/docusaurus-plugin-google-analytics/src/index.ts

@@ -18,21 +18,21 @@ import type {PluginOptions, Options} from './options';
 export default function pluginGoogleAnalytics(
   context: LoadContext,
   options: PluginOptions,
-): Plugin {
+): Plugin | null {
+  if (process.env.NODE_ENV !== 'production') {
+    return null;
+  }
+
   const {trackingID, anonymizeIP} = options;
-  const isProd = process.env.NODE_ENV === 'production';
 
   return {
     name: 'docusaurus-plugin-google-analytics',
 
     getClientModules() {
-      return isProd ? ['./analytics'] : [];
+      return ['./analytics'];
     },
 
     injectHtmlTags() {
-      if (!isProd) {
-        return {};
-      }
       return {
         headTags: [
           {

packages/docusaurus-plugin-google-gtag/src/index.ts

@@ -32,8 +32,10 @@ function createConfigSnippets({
 export default function pluginGoogleGtag(
   context: LoadContext,
   options: PluginOptions,
-): Plugin {
-  const isProd = process.env.NODE_ENV === 'production';
+): Plugin | null {
+  if (process.env.NODE_ENV !== 'production') {
+    return null;
+  }
 
   const firstTrackingId = options.trackingID[0];
 
@@ -45,13 +47,10 @@ export default function pluginGoogleGtag(
     },
 
     getClientModules() {
-      return isProd ? ['./gtag'] : [];
+      return ['./gtag'];
     },
 
     injectHtmlTags() {
-      if (!isProd) {
-        return {};
-      }
       return {
         // Gtag includes GA by default, so we also preconnect to
         // google-analytics.

packages/docusaurus-plugin-google-tag-manager/src/index.ts

@@ -16,10 +16,12 @@ import type {PluginOptions, Options} from './options';
 export default function pluginGoogleAnalytics(
   context: LoadContext,
   options: PluginOptions,
-): Plugin {
-  const {containerId} = options;
-  const isProd = process.env.NODE_ENV === 'production';
+): Plugin | null {
+  if (process.env.NODE_ENV !== 'production') {
+    return null;
+  }
 
+  const {containerId} = options;
   return {
     name: 'docusaurus-plugin-google-tag-manager',
 
@@ -28,9 +30,6 @@ export default function pluginGoogleAnalytics(
     },
 
     injectHtmlTags() {
-      if (!isProd) {
-        return {};
-      }
       return {
         preBodyTags: [
           {

packages/docusaurus-plugin-pwa/src/index.ts

@@ -19,8 +19,6 @@ import type {PluginOptions} from '@docusaurus/plugin-pwa';
 
 const PluginName = 'docusaurus-plugin-pwa';
 
-const isProd = process.env.NODE_ENV === 'production';
-
 function getSWBabelLoader() {
   return {
     loader: 'babel-loader',
@@ -45,12 +43,21 @@ function getSWBabelLoader() {
 export default function pluginPWA(
   context: LoadContext,
   options: PluginOptions,
-): Plugin<void> {
+): Plugin<void> | null {
+  if (process.env.NODE_ENV !== 'production') {
+    return null;
+  }
+  if (context.siteConfig.future.experimental_router === 'hash') {
+    logger.warn(
+      `${PluginName} does not support the Hash Router and will be disabled.`,
+    );
+    return null;
+  }
+
   const {
     outDir,
     baseUrl,
     i18n: {currentLocale},
-    siteConfig,
   } = context;
   const {
     debug,
@@ -61,13 +68,6 @@ export default function pluginPWA(
     swRegister,
   } = options;
 
-  if (siteConfig.future.experimental_router === 'hash') {
-    logger.warn(
-      `${PluginName} does not support the Hash Router and will be disabled.`,
-    );
-    return {name: PluginName};
-  }
-
   return {
     name: PluginName,
 
@@ -79,7 +79,7 @@ export default function pluginPWA(
     },
 
     getClientModules() {
-      return isProd && swRegister ? [swRegister] : [];
+      return swRegister ? [swRegister] : [];
     },
 
     getDefaultCodeTranslationMessages() {
@@ -90,10 +90,6 @@ export default function pluginPWA(
     },
 
     configureWebpack(config) {
-      if (!isProd) {
-        return {};
-      }
-
       return {
         plugins: [
           new webpack.EnvironmentPlugin({
@@ -111,37 +107,31 @@ export default function pluginPWA(
 
     injectHtmlTags() {
       const headTags: HtmlTags = [];
-      if (isProd) {
-        pwaHead.forEach(({tagName, ...attributes}) => {
-          (['href', 'content'] as const).forEach((attribute) => {
-            const attributeValue = attributes[attribute];
-
-            if (!attributeValue) {
-              return;
-            }
-
-            const attributePath =
-              !!path.extname(attributeValue) && attributeValue;
-
-            if (attributePath && !attributePath.startsWith(baseUrl)) {
-              attributes[attribute] = normalizeUrl([baseUrl, attributeValue]);
-            }
-          });
-
-          return headTags.push({
-            tagName,
-            attributes,
-          });
+      pwaHead.forEach(({tagName, ...attributes}) => {
+        (['href', 'content'] as const).forEach((attribute) => {
+          const attributeValue = attributes[attribute];
+
+          if (!attributeValue) {
+            return;
+          }
+
+          const attributePath =
+            !!path.extname(attributeValue) && attributeValue;
+
+          if (attributePath && !attributePath.startsWith(baseUrl)) {
+            attributes[attribute] = normalizeUrl([baseUrl, attributeValue]);
+          }
+        });
+
+        return headTags.push({
+          tagName,
+          attributes,
         });
-      }
+      });
       return {headTags};
     },
 
     async postBuild(props) {
-      if (!isProd) {
-        return;
-      }
-
       const swSourceFileTest = /\.m?js$/;
 
       const swWebpackConfig: Configuration = {

packages/docusaurus-plugin-sitemap/src/index.ts

@@ -17,12 +17,12 @@ const PluginName = 'docusaurus-plugin-sitemap';
 export default function pluginSitemap(
   context: LoadContext,
   options: PluginOptions,
-): Plugin<void> {
+): Plugin<void> | null {
   if (context.siteConfig.future.experimental_router === 'hash') {
     logger.warn(
       `${PluginName} does not support the Hash Router and will be disabled.`,
     );
-    return {name: PluginName};
+    return null;
   }
 
   return {

packages/docusaurus-plugin-vercel-analytics/src/index.ts

@@ -11,14 +11,15 @@ import type {PluginOptions, Options} from './options';
 export default function pluginVercelAnalytics(
   context: LoadContext,
   options: PluginOptions,
-): Plugin {
-  const isProd = process.env.NODE_ENV === 'production';
-
+): Plugin | null {
+  if (process.env.NODE_ENV !== 'production') {
+    return null;
+  }
   return {
     name: 'docusaurus-plugin-vercel-analytics',
 
     getClientModules() {
-      return isProd ? ['./analytics'] : [];
+      return ['./analytics'];
     },
 
     contentLoaded({actions}) {

packages/docusaurus-types/src/plugin.d.ts

@@ -191,7 +191,10 @@ export type LoadedPlugin = InitializedPlugin & {
 export type PluginModule<Content = unknown> = {
   (context: LoadContext, options: unknown):
     | Plugin<Content>
-    | Promise<Plugin<Content>>;
+    | Promise<Plugin<Content>>
+    | null
+    | Promise<null>;
+
   validateOptions?: <T, U>(data: OptionValidationContext<T, U>) => U;
   validateThemeConfig?: <T>(data: ThemeConfigValidationContext<T>) => T;
 

packages/docusaurus/src/commands/swizzle/context.ts

@@ -6,22 +6,41 @@
  */
 
 import {loadContext} from '../../server/site';
-import {initPlugins} from '../../server/plugins/init';
+import {initPluginsConfigs} from '../../server/plugins/init';
 import {loadPluginConfigs} from '../../server/plugins/configs';
-import type {SwizzleCLIOptions, SwizzleContext} from './common';
+import type {SwizzleCLIOptions, SwizzleContext, SwizzlePlugin} from './common';
+import type {LoadContext} from '@docusaurus/types';
+
+async function getSwizzlePlugins(
+  context: LoadContext,
+): Promise<SwizzlePlugin[]> {
+  const pluginConfigs = await loadPluginConfigs(context);
+  const pluginConfigInitResults = await initPluginsConfigs(
+    context,
+    pluginConfigs,
+  );
+
+  return pluginConfigInitResults.flatMap((initResult) => {
+    // Ignore self-disabling plugins returning null
+    if (initResult.plugin === null) {
+      return [];
+    }
+    return [
+      // TODO this is a bit confusing, need refactor
+      {
+        plugin: initResult.config,
+        instance: initResult.plugin,
+      },
+    ];
+  });
+}
 
 export async function initSwizzleContext(
   siteDir: string,
   options: SwizzleCLIOptions,
 ): Promise<SwizzleContext> {
   const context = await loadContext({siteDir, config: options.config});
-  const plugins = await initPlugins(context);
-  const pluginConfigs = await loadPluginConfigs(context);
-
   return {
-    plugins: plugins.map((plugin, pluginIndex) => ({
-      plugin: pluginConfigs[pluginIndex]!,
-      instance: plugin,
-    })),
+    plugins: await getSwizzlePlugins(context),
   };
 }

packages/docusaurus/src/server/plugins/__tests__/init.test.ts

@@ -24,7 +24,7 @@ async function loadSite(
 describe('initPlugins', () => {
   it('parses plugins correctly and loads them in correct order', async () => {
     const {context, plugins} = await loadSite('site-with-plugin');
-    expect(context.siteConfig.plugins).toHaveLength(6);
+    expect(context.siteConfig.plugins).toHaveLength(7);
     expect(plugins).toHaveLength(10);
 
     expect(plugins[0]!.name).toBe('preset-plugin1');
@@ -85,4 +85,13 @@ describe('initPlugins', () => {
       Note that even inline/anonymous plugin functions require a 'name' property."
     `);
   });
+
+  it('throws user-friendly error message for plugins returning undefined', async () => {
+    await expect(() => loadSite('site-with-undefined-plugin')).rejects
+      .toThrowErrorMatchingInlineSnapshot(`
+      "A Docusaurus plugin returned 'undefined', which is forbidden.
+      A plugin is expected to return an object having at least a 'name' property.
+      If you want a plugin to self-disable depending on context/options, you can explicitly return 'null' instead of 'undefined'"
+    `);
+  });
 });